3. Gene Structure Expression and Regulation Flashcards
What is a gene?
A segment of DNA that codes for proteins
What is the template strand?
Template strand of DNA contains the coded information of a particular gene, also called antisense or non coding strand.
What is the complementary strand?
The non template strand or the sense strand or the coding strand.
What is the coding region?
The coding region is the part of a gene that contains coded information for making a protein. In eukaryotic cells it is not continuous.
What are introns and exons?
Introns are non coding regions of DNA and exons are coding regions of DNA
What is the central dogma of molecular genetics?
The idea that DNA makes proteins by way of an intermediate RNA. Information can only flow from DNA to proteins
What is transcription?
It is the process of copying the genetic instructions present in the DNA to messenger RNA. Occurs in the nucleus of eukaryotic organisms and in the cytoplasm of prokaryotic organisms.
What are the steps in transcription?
- the enzyme RNA polymerase binds to a specific base sequence of the DNA template strand of the promoter region of a gene to be transcribed,
- the DNA unwinds and exposes the bases of the template strand,
- the base sequence of the DNA template strand (3’ to 5’) guides the formation of a complementary copy of mRNA. Free complementary RNA nucleotides pair with DNA and are joined together one by one to form a chain of mRNA or premrna in eukaryotes.
- the enzyme RNA polymerase catalysers this reaction adj copies the DNA until it reaches a stop signal, terminating RNA production
- a single stranded molecule of mRNA or premrna results adm is complementary to the base sequence of the DNA strand
- mRNA transcript or premrna is released and the double helix reforms.
What happens in pre-mRNA processing in eukaryotes?
- a methylated cap is added
- a poly a tail is added
- introns are spliced out
What is translation?
Translation is the process of decoding the genetic instructions where the order of bases in the mRNA transcript is used to produce a specific polypeptide amino acid chain.
Where does translation occur?
Occurs in the cytoplasm at the ribosomes of both eukaryotic and prokaryotic organisms
What is rRNA?
Produced in large quantities in the nucleus and stored there to form the nucleolus. rRNA moves from the nucleus to the cytoplasm when it is required to form part of ribosomes. Binds to proteins to make ribosomes.
What structures are required for translation?
- mRNA carries the code from the DNA and contains codons.
- tRNA is responsible for transporting amino acids to their correct position on the mRNA and contains anti codons.
- ribosomes: provides the environment for tRNA attachment and amino acid linkage
- pool of amino acids
What are the steps in translation?
- the mRNA carrying the code transcribed from DNA is transported from the nucleus through the nuclear pore to the ribosome in the cytoplasm.
- the small ribosomal subunit bonds to the methylated cap on the mRNA and scans along the mRNA for an Aug. Once found, a large ribosomal subunit joins with the small one commencing translation when a start codon is translated.
- a tRNA molecule with the complementary anti codon pairs momentarily with the mRNA releasing its amino acid.
- as the ribosome moves along the mRNA more amino acids are added to the growing polypeptide chain and peptide bonds between adjacent amino acids form, catalysed by enzymes in the ribosomes.
- when the ribosome reaches a stop codon protein synthesis stop and the polypeptide chain is released.
What does the order of nucleotides determine?
The order of nucleotides in DNA determines the order of nucleotides in mRNA which determines the tRNA that will bind to the mRNA which in turn determines the order of the amino acids linked together to produce a protein.
